Great Wall of China more than twice as long as previous estimates

Rain clouds pass over a section of the Great Wall at Jinshanling, Hebei Province on Sunday, June 10.

According to a recent BBC News report, the wall, which is a series of fortifications made of stone, brick and rammed earth, was subject to a recent archaeological survey that found its total length to be 21,196 km or 13,171 miles. Based on a 2009 study, it was thought to be much shorter at 8,850 km. The Great Wall, which was built in 500 BC to protect China's northern border, is the world's largest manmade structure. Read more.

Ed Jones / AFP - Getty Images

A tourist walks over a section of the Great Wall at Jinshanling, Hebei Province on June 10.

Ed Jones / AFP - Getty Images

Tourists look out from a section of the Great Wall at Jinshanling, Hebei Province on June 10.